Run tests in portable mode in a separate step

.github/workflows/test.yml

@@ -47,6 +47,12 @@ jobs:
         python -m pip install --upgrade pip
         pip install wheel
         pip install -r requirements.txt
+    - name: Portable run
+      if: ${{ matrix.os == 'ubuntu-18.04' && matrix.python-version == '2.7' }}
+      run: |
+        python -m pybitmessage.bitmessagemain -t
+    - name: Install
+      run: |
         python setup.py install
     - name: Install additional python dependencies
       if: ${{ matrix.python-version == '3.8' }}